原式=[(x+2)-(x-2)]/(x+2)(x-2)+(x2-4x)/(x+2)(x-2)
=4/(x+2)(x-2)+(x2-4x)/(x+2)(x-2)
=(x2-4x+4)/(x+2)(x-2)
=(x-2)2/(x+2)(x-2)
==(x-2)/(x+2)